Differential conductivity methods for carrying out analytical determinations are known as exemplified by U.S. Pat. Nos. 3,607,083 and 3,950,137. These methods depend typically on the addition of reagents to precipitate interfering ions. As such, the methods tend to be useful for only a relatively few species. Accumulation of the precipitate also produces messy instrument clean-up and fouling problems. Thus, the technique is generally little favored where alternate methods are available, and particularly so for on-line automated, and thus substantially unattended, analysis systems.
Known ion-exchange chromatographic analytical techniques are also pertinent to the inventive subject matter since the chemical reactions performed may be similar to that practiced by the invention. The prior art is represented by the teachings of U.S. Pat. No. 3,920,397. The invention is distinguished from the referenced ion-exchanged chromatographic technique since the latter is designed using basic or acidic carrier phases selected on the criteria of suitability to separate certain defined ion species, the carrier being ultimately converted to water. Hence, the conversion of the species of interest to water is not followed or predisposed by this technique. In addition, the technique is unsuitable for assaying acid and base samples directly, and is designed rather for detecting and quantitating chromatographically separated cation and anion species.
What the art refers to as total ionic content analyzers and single ion analyzers also relate to the invention since the techniques employ conductimetric detectors, in conjunction with ion-exchange derivatization steps. Examples of this prior art are published in U.S. Pat. Nos. 3,897,213, 3,915,642 and 3,918,906. These methods are generally characterized by the conversion of a mixture of ionic species to a single, preselected species. The step is used to maximize the accuracy of a conductimetric measurement. The invention is thus distinguished over these quite different methods neither designed or suitable for the quantitative analysis of acid and base species in acid/salt and base/salt sample matrices.
Titration of strong acid and base solutions is also considered pertinent prior art from a comparative standpoint. Thus, current industrial process stream monitoring techniques often favor automatic titration analysis for strong and moderately strong base and acid determinations. However, automated titration instrumentation is expensive and tends to require a laborious maintenance schedule. Thus, there is a need to develop a simpler, more reliable instrument and technique for the quantitative analysis of acid and base samples which contain interfering salt(s).